The construction of very large phage displayed antibody repertoires is an indispensable step towards rapidly and easily producing high affinity antibodies. Although several interesting antibodies have been discovered thus far using phage display, there still exists a need to improve this technology, primarily due to the low diversity and small library size achieved using current methods. The goal of the present proposal is to produce large highly diverse antibody display libraries and to use these libraries for the isolation of human antibodies against interleukin-5 (IL-5). To accomplish this the investigators plan to use combinatorial infection followed by in vivo recombination to achieve large diverse (1011 clones) libraries. In vivo recombination will be carried out using the non-reversible site specific recombination system of phage lambda. Functional heavy and light chain sequences will be incorporated into these libraries using a novel strategy which pre-selects only those human antibody sequences which are expressed and secreted in E. coli. The resulting antibody display libraries will be screened by panning phage against immobilized human IL-5. Specific antibodies will be tested for neutralizing activity. Anti-IL-5 could prove to be a valuable therapeutic for asthma. Advanced clinical trials using a humanized mouse anti-IL-5 have prevented eosinophil inflammation and airway construction in primates. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE